DESCRIPTION: The fundamental goal of this renewal application is the discovery of new methods to control molecular aggregation using hydrogen bonding and pi-stacking interactions. It is noted that the simplest aggregates to be studied are disc- and washer-shaped structures composed of six heterocyclic building blocks called "tectons." The tectons are said to self-associate as a result of complementary hydrogen bonding arrays on remote edges of the hetero-aromatic systems. Two strategies for generating higher levels of self-assembly are to be investigated. It is stated that the first is through pi-stacking of disc- and washer- shaped aggregates in solution or in the solid-state, forming columnar- tubular structures and that the second is by addition of an optically active, "end-capping" heterocycle that will induce formation of a continuous pi-stacked and hydrogen bonded helical structure. This assembly process is said to be similar to the disc to lock-washer to helix transition used by the tobacco mosaic virus protein in forming the viral capsid. It is noted that an alternative approach to helical structures uses heterocyclic units with geometries that prevent closure to form discs or washers. Endo-cyclic substituents attached to the heteroaromatic compounds are to be oriented toward the center of the disc (washer), while a second set of exo- cyclic substituents are to project out from its periphery. It is noted that the internal groups determine the size and chemical nature of the interior of the column or tube, while the peripheral substituents adjust the morphology and properties of the aggregate, including its solubility and crystallinity. The principal investigator notes that two other self-assembling systems that will be studied are a self-assembling dendrimer and a molecular "box." He indicates that the latter assembly is intrinsically size- limited by forming a cyclic structure, whereas the dendritic assembly is limited by sterics on its periphery as it grows in a non-linear fashion. It is stated that all assembly processes in this proposal have biological analogies, and are designed to be functional by virtue of channels and cavities that can encapsulate molecules. It is finally indicated that applications include: (1) biomimetic viral capsids for solution encapsulation (e.g., drug-delivery), (2) designed clathrates for separation, purification, and/or optical resolution of drugs and other organic compounds, (3) devices for the storage of small quantities of toxic materials, and (4) mimics of protein pores.